NHS acute trusts were asked by BBC Radio 4's You and Yours programme for figures for Wednesday 4 December 2013, and the weekend of 7 and 8 December.

The figures also showed a difference in terms of the grades of doctors on duty.

Hospitals in England had an average of 86 consultants on a Wednesday, compared to just over eight in the afternoon at the weekend.

One medium-sized hospital, St Marys on the Isle of Wight, had 63 consultants in the building during the week, but none on a weekend afternoon.

The hospital said it had 12 consultants on call who could come in.

Blood tests

The NHS published its last figures about patient mortality in 2011.

The survey of 14 million admissions showed that a patient is 11% more likely to die if admitted on a Saturday and 16% more likely to die if admitted on a Sunday than during the week.

The NHS also reports on patient outcomes.

There are not enough trainees in the system to deliver the kind of seven day service that we would all like to seeDr Peter Williams, Royal Liverpool Hospital

Overall, patients stay longer in hospital when they are admitted at weekends.

They wait longer for a diagnosis and part of the reason for that is that there are not the senior doctors around in the departments that do the blood tests, X-rays and scans.

Prof Sir Bruce Keogh has set out a 10-point plan to achieve 24-hour, seven day a week staffing in hospitals. He wants to see it in place by 2017.

He told You and Yours: "It's a bold plan because the NHS, like other parts of society, has not functioned the same at the weekend as it has in the week - but we need to do it with urgency.

"The rest of society has moved on, all other service industries are starting to address how they provide more routine services at the weekend and it's time we did so in health".

But Sir Richard Thompson of the Royal College of Physicians thinks it will take longer.

"I think we're heading in the right direction but I think the plan is optimistic. Without getting a large extra number of staff of all grades and all types I cannot see how we can get a full equal service on Monday, Tuesday, Wednesday, Thursday, Friday, Saturday and Sunday".

'Bit of a rest'

According to the research the Royal Liverpool Hospital has 7% of the level of staffing for doctors at the weekend compared to a Wednesday afternoon.

Sharon Duffy has been a patient on the haematology ward at the hospital for six weeks.

"It's quiet at the weekend but everything is still available. There is no anxiety because there's always a button to press. There is just less staff - if anything it's a bit of a rest"

The hospital's medical director, Dr Peter Williams, said that while its mortality rates do not change at the weekend, the whole system needs to be improved.

"We've got to change the balance of the service between the junior doctors and the senior doctors.

"There are not enough trainees in the system to deliver the kind of seven day service that we would all like to see".

Another sticking point for Dr Williams is the attitude of staff:

"There may be some reluctance. It becomes more difficult when you tell people they will be on call 24/7 on site. That's a big step.

"Some of our specialties have already done it, but if I'm going out to consultants in their late 40s and 50s and saying, 'I know you've been on your contract for 15 years, but I would now like you to be up all night on a Saturday or Sunday', that's a big ask".

Dean Royles, chief executive of NHS Employers, said changes were needed to consultant doctors' contracts to make working at weekends more cost effective for the NHS.

However, Dr Mark Porter, chairman of the British Medical Association, said structural change was needed across the service. He stressed that the NHS worked to safety standards formulated by the medical Royal Colleges.

The BBC investigation sent Freedom of Information requests to all of the NHS acute trusts in the UK and received full responses from more than half of them.